获取子级的值

const person = {
  name: 'John',
  age: 30,
  address: {
    city: 'New York',
    country: 'USA'
  }
};

const address = person.address;
console.log(address); // 输出：{ city: 'New York', country: 'USA' }

const address = person['address'];
console.log(address); // 输出：{ city: 'New York', country: 'USA' }

const city = person.address.city;
console.log(city); // 输出：'New York'

const city = person['address']['city'];
console.log(city); // 输出：'New York'

const numbers = [1, 2, 3, 4, 5];

const value = numbers[2];
console.log(value); // 输出：3